(1) Field of the Invention
The present invention relates to a pressure sensing device which can be utilized for shift position control of information processing equipment, office equipment, industrial equipment, home equipment, electronic equipment, building, automobile, vessel and so forth, pressure control actuated on a pressure source such as fluid pressure, air pressure and the like, and also for detection means for automatically detecting size, weight and so forth.
(2) Description of the Prior Art
FIG. 6 shows a known pressure sensing device in which an armored case 1 is provided on an electrode substrate 2 together with a pair of electrodes 21a, 21b and an actuator (or plunger) 3. A high molecular conductor 4 and a compression spring 5 are contained in the armored case 1. The high molecular conductor 4 and the electrodes 21a, 21b are normally kept non-contacted by the compression spring 5.
Then, a guide hole 11 is perforated in the armored case 1, a shaft 31 protruding from the center of the actuator 3 is inserted therein to pass externally, and a top or nose portion 33 of the shaft 31 is formed as an external force receiving part.
In the prior art construction described above, when an external force is given to the nose portion 33 of the actuator 3, the actuator 3 descends against a tension of the spring 5, the high molecular conductor 4 provided on the actuator 3 comes in contact with the electrodes 21a, 21b and thus is conductive to function as an electric switch.
Then, upon releasing the external force to the actuator 3, the high molecular conductor 4 is isolated from the electrodes 21a, 21b by a retaining strength of the spring 5, thus opening the switch.
The prior art exemplified as above comprises one kind of switch wherein contacts wrought with a high molecular conductor are disposed in opposition so as to keep a space with the electrodes at all times through spring or other means. The contacts of the molecular conductor are brought into contact with the electrodes when an external force is applied thus causing an electrical signal. However, using this as a detecting part involves various problems such that (1) the distance between the electrode and the contact must be shortened or a spring force must be weakened for securing high sensitivity, which may result in causing an erroneous operation due to vibration or other reason and losing a reliability, (2) a displacement called after stroke is necessary for detecting a position of matters in transit as it is difficult to stop the matters moving suddenly after the position is detected, however, the displacement as after stroke cannot be secured thoroughly, (3) dispersion and secular change of the contact resistance value due to external force are heavy, and that (4) since a space is formed, a deterioration due to incoming of dust and dirt cannot be avoided.
The invention has been done in view of the aforementioned defects, and its object is to provide a pressure sensing device which is capable of replacing a change in pressure with an electrical signal by utilizing characteristics of a high molecular conductor.